Tire non-uniformity relates to the symmetry (or lack of symmetry) relative to the tire's axis of rotation in certain quantifiable characteristics of a tire. Conventional tire building methods realistically have many opportunities for producing non-uniformities in tires. During rotation of the tires, non-uniformities present in the tire structure produce periodically-varying forces at the wheel axis. Tire non-uniformities are important when these force variations are transmitted as noticeable vibrations to the vehicle and vehicle occupants. These forces are transmitted through the suspension of the vehicle and may be felt in the seats and steering wheel of the vehicle or transmitted as noise in the passenger compartment. The amount of vibration transmitted to the vehicle occupants has been categorized as the “ride comfort” or “comfort” of the tires.
Tire uniformity characteristics, or attributes, are generally categorized as dimensional or geometric variations (radial run out (RRO) and lateral run out (LRO)), mass variance, and rolling force variations (radial force variation, lateral force variation and tangential force variation, sometimes also called longitudinal or fore and aft force variation). Uniformity measurement machines often measure the above and other uniformity characteristics by measuring force at a number of points around a tire as the tire is rotated about its axis. Geometric variations are usually measured as deviations from an average dimension. Mass variance measurement is typically limited to mass unbalance, which is the first harmonic component of mass variance. Mass unbalance can be measured statically on a balance device or on a device that rotates the tire with respect to an axis passing through the geometric center of the tire without applying a load to the tire.
Measurement of tire uniformity is typically done for quality control after manufacturing the tire to determine the effect the non-uniformities will have on a vehicle, that is, the vibrations that will be produced by the non-uniformities. The measurement can be used, for example, to reject tires or to sort or grade tires according to the vehicle for which the tire will be used. Correction procedures can also be performed to account for some of the non-uniformities by making adjustments to the manufacturing process. Additional correction techniques can be performed to address non-uniformities of a cured tire including, but not limited to, the addition and/or removal of material to a cured tire and/or deformation of a cured tire.
High speed uniformity of tires has become a growing concern in the automobile industry. High speed uniformity testing can involve performing uniformity measurements while rotating the tire at speeds approximating highway speeds. Uniformity measurements performed as part of high speed uniformity testing are typically performed at multiple discrete rotational speeds. Multiple rotations of the tire can be required at each discrete speed to obtain sufficient data for analyzing high speed uniformity characteristics. As a result, it can require a considerable amount of time (e.g. up to 30 minutes) to cover a larger speed range. Consequently, only a few and fairly widely spaced discrete speeds are typically used for high speed uniformity measurements of a tire.
Thus, a need exists for an improved method of performing high speed uniformity measurements of tires.